Spatial accumulation of salicylic acid is in effector-triggered immunity of potato against viruses regulated by RBOHD

While activation of resistance (R) proteins has been intensively studied, the mechanisms acting downstream of R protein activation remain elusive. We studied effector-triggered immunity (ETI) conditioned by the potato Ny-1 gene against potato virus Y. Transcriptomic, ultrastructural and biochemical analyses of four consecutive tissue sections in and surrounding the foci of viral infection at three different lesion developmental stages revealed processes that are spatiotemporally regulated. The transcriptional response in the cell death zone and surrounding tissue is dependent on SA. For some of the genes, spatiotemporal regulation is completely lost while for others, the regulation is different in SA-deficient line indicating multiple connections between hormonal signaling modules. The induction of RBOHD NADPH oxidase expression, together with expression of Thioredoxin H gene, occurs specifically in the border region of the lesion during ETI. In plants with silenced RBOHD, ETI is perturbed and virus spread is not arrested at the site of infection. Expression of RBOHD is under the control of SA. On the other hand, RBOHD activity is required for spatial regulation of SA accumulation. We identified an UDP-glucosyltransferase, encoding an enzyme involved in feedback activation of SA biosynthesis, that is derepressed at the border of the lesion in RBOHD silenced plants. Altogether, we revealed a novel aspect of viral ETI, the RBOHD-SA feedback loop required for its spatial regulation.